抽象类

unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs;

type
  TForm1 = class(TForm)
    procedure FormCreate(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

//夫类，抽象类
  TParent = class
  protected
    function MyFun(i: Integer): Integer; virtual; abstract;
    //抽象方法(纯虚方法)，只有定义没有实现，一个类包含一个即成抽象类，抽象类不能直接创建对象。
  end;

//子类
  TChild = class(TParent)
  protected
    function MyFun(i: Integer): Integer; override;  //覆盖
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

{ TChild }

function TChild.MyFun(i: Integer): Integer;
begin
  Inc(i);
  Result := i;
end;

//测试
procedure TForm1.FormCreate(Sender: TObject);
var
  p: TParent;
  c: TChild;
begin
  p := TChild.Create;  //抽象类只能通过其子类创建对象
  c := TChild.Create;

  ShowMessage(IntToStr(p.MyFun(2)));  //3
  ShowMessage(IntToStr(c.MyFun(2)));  //3

  p.Free;
  c.Free;
end;

end.